I've got a casing made of Inconel 718. Its been through a solution and re-age heat treatment (solution just short of 1000oC, reage around 700oC) and I've found some areas of plasma from previous repairs. Does running the part through these heat treatments damage the existing plasma coating and do I need to renew it? I always thought that these high temp runs does damage the coating and renewing them is mandatory. Is this the case?

"Renewing them is mandatory" I think will be the case in the majority of aero work. But, this does not necessarily mean that the coatings involved will be damaged, just that they are not proven fit for purpose. I have looked at a few Chromium carbide/nickel chromium coatings after similar heat treatments and from metallography they looked better than the originals. Certainly, a few coatings like T800 have been shown to improve after heat treatment. I think this is down to a slight sintering effect, giving slightly improved density and better inter-particle bonding.

thanks for the response. It maybe that I'm basing my judgement on coated parts which have been through furnace braze and halo cleaning. These were very high temp runs (1190oC), taking the part near to its melting point.

For me, I work on repair manual and serviceable or repairable limits, after heat treatment, we normally will re-inspect on the coating and see if there is visual chippings, flake off..debond..etc, if it iswithin the limit, we will try to protect the coating to continue for other repair.

Ofcourse that is based on our application and the parts we work on. Focusing on customer need, if the repair can be minimized, or reduced workscope, it means cost saving for the customers =)